This SBIR project will develop a rapid, high resolution optical imaging method for clinical and biomedical applications including imaging of arterial and venous structures s atherosclerotic plaques, detection of cancerous and pre-cancerous tissues, optical guidance during microsurgery and optical biopsy. The method, complex differential spectral interferometry (CDSI), is a frequency domain optical tomography method that is an improvement over both time domain optical coherence tomography (OCT) and spectral interferometry (SI). Like these other methods, CDSI can be easily used with fiber optics and incorporated into endoscopes, catheters and similar devices for in vivo applications. However, CDSI instrumentation is less complex, has I faster imaging rates and a potentially better dynamic range. Ultimately, an imaging system that provides I both spectroscopic and structural information with ten micrometer or better resolution will be developed for in vivo diagnostic imaging and tissue biopsy.